Frequency responsive electronic lock mechanism



Nov. 10, 1970 c. A. IRAZOQUI 3,539,991

7 FREQUENCY RESPONSIVE ELECTRONIC LOCK MECHANISM Filed July 18,- 1967 C 3 Sheets-Sheet 1 INVENTOR (news A. Imzopu/ BY I ATTORNEYS Nov. 10, 1970 v c. A. IRAZOQUI 3,539,991

FREQUENCY RESPONSIVE ELECTRONIC LOCK MECHANISM Filed July 18, 1967 3 Sheets-Sheet 5 IZ' Q10 3 I N VENTOR ATTORNEYS Patented Nov. 10, 1970 US. Cl. 340-171 8 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to an actuating system responsive to a coded electrical signal. The invention may be particularly adapted for use as a locking system on a parking meter or some other similar device. In such an embodiment a portable encoder is provided which includes both a battery or other power source for providing an operating voltage, and a generator for producing coded electrical signals. The coin box on the parking meter is provided with a lock mechanism which may be selectively opened, in response to the proper coded signal, by the operating voltage from the encoder. A flexible electric cord is attached to the encoder and may be plugged into a suitable receptacle in the parking meter to complete the electrical circuits between the encoder and meter. Installed within the meter box is a decoder circuit which senses the presence of a coded signal and emits a command signal in response thereto. The command signal is returned to the encoder via a feedback circuit and causes the operating voltage to be supplied to the lock mechanism to open it. A logic circuit is provided as part of the decoder circuit in order to inhibit the system from operating should the operating voltage be applied before the coded signal or should an incorrect coded signal be applied. The coded signals may take the form of one or more electrical signals of different frequency or may include a series of coded digital signals.

BACKGROUND OF THE INVENTION The present invention relates to an electrical code responsive actuating device in which the power to operate the system may be supplied from an encoding device, to which the actuator is connected at such time as it is to be operated. The actuator may be one of numerous electrically responsive or electromechanical devices employed for various purposes, for example, as a locking mechanrsm.

In the prior art many electrical lock controlling systems have been developed to bar unauthorized access to locked areas and still enable easy access to persons having a proper key or combination to operate the system. One common type of such system contemplates the use of an electrical circuit, for example, an oscillator circuit, which may be energized to render a utilization or unlocking circuit operative. In the system an essential impedance element of the oscillator circuit is molded into a removable assembly or key which may be manually connected into the circuit by suitable terminals or contacts. Insertion of a key component of a preselected value causes the completed circuit to oscillate at a particular frequency. A discriminating circuit in the system responds to that preselected frequency and triggers a power circuit which energizes the utilization circuit. When a component of other than the preselected value is inserted, the oscillator generates a signal which is eliminated by the discriminating circuit, no trigger pulse is emitted, and the utilization circuit remains de-energized.

In a variation of this type of system the oscillatory circuit described above is replaced by a circuit having a pair of relay coils in series connection with a source and the key element. One of the relay coils is designed to operate at a certain minimum current flow, which will result when a key element of specific value is inserted, to close a set of contacts which will energize the utlization circuit. The second relay is designed to operate at a higher current flow, caused by a value of impedance lower than the predetermined specific value, to open a second set of contacts and de-energize the utilization circuit. Thus, such a system is also designed to be energized only in response to a key having an impedance within a predetermined range of values.

Although the above types of circuits will function satisfactorily in some applications, they are inherently subject to certain disadvantages. For example, in these systems the impedance key is the only removable or portable element; the power source and discriminating circuitry normally being built into the device as part of the locking system. This means that batteries must be continually replaced or that some other source of power must be provided at the location of each locking mechanism. Furthermore, most systems of the type discussed above require the use of a separate key for each different combination or lock. Both these features impose limitations when it is desired that a single authorized operator be able to open and service a plurality of widely spaced locked receptacles within a short time. For example, the requirements of a locking system for a group of parking meters could not be satisfactorily fulfilled by one of the above mentioned systems. The cost of installing a lock on each parking meter which included a complicated electrical circuit, as well as a battery or other power source, would be prohibitive. In addition, it is preferable if an operator servicing such a meter system can operate each lock with the same key device, while still preserving the integrity of the system should a key device fall into unauthorized hands. This requires that one key be capable of adjustment in order to open a plurality of locks having different combinations.

SUMMARY OF THE INVENTION The present invention provides a relatively simple, low cost electrical code responsive actuating device. This electrically responsive actuating device may be easily adapted as the movable element in a locking system or may be used in any other application where it is desired to control an electrically responsive element such as a solenoid, magnetic latch, or signal light in response to a preselected electrical code or condition. The actuating device is associated with a decoder circuit which permits energization of the actuator only in response to a predetermined coded signal. The power to operate the actuator may be supplied from a source in an encoder circuit which may be adjusted to generate the predetermined code signal. The encoder and decoder may be structurally separate devices coupled together by a flexible electrical cord or other conduit whenever it is desired to complete an electrical circiut therebetween in order to energize and operate the system. In this way a single encoder device may be adapted to produce a plurality of different coded signals and used to operate a like plurality of actuators, each of which is responsive to a different coded signal. Upon reception of its predetermined coded signal each decoder sends back a command signal to the encoder which triggers the supply of the operating power from the encoder to the actuator. In the absence of the proper coded signal or in case the operating power is applied prior to the coded signal, the actuator is inhibited from operation. The coded signals may take various forms. In the preferred embodiment of the invention the code signal is made up of three sine waves of different frequency. The presence of these three frequencies is detected in the decoder by an equal number of tuned amplifier stages. However, the coded signal could, as well, be comprised of sine Waves of staggered phase or a coded train of digital pulses. In the latter cases, the decoder would then include suitable phase discriminating circuitry or digital logic circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS The novel features of the invention are set forth in particular in the appended claims. The invention itself, both as to its construction and manner of operation, together with additional objects and advantages thereof, will be best understood from the following description of a preferred embodiment when read in conjunction with the accompanying drawings in which:

FIG. 1 is a diagrammatic view showing the present invention adapted for use as a locking system for a parking meter;

FIG. 2 is a schematic drawing and block diagram of a complete system illustrating the method and apparatus of the present invention;

FIG. 3 is a schematic diagram of an oscillator circuit which may be employed in the code generating apparatus of the disclosed embodiment of the invention;

FIG. 4 is a schematic diagram of a mixer circuit which may be employed in the encoder of the disclosed embodiment of the invention; and

FIG. 5 is a schematic diagram showing a particular embodiment of detector and logic circuitry which may be used in the decoder of the disclosed embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a typical parking meter head 1 is shown mounted on a stand 2. The meter head includes an internal timing mechanism, not shown, which drives an indicating arm 3 in relation to a dial 4. A removable front cover 6 includes a coin slot 7 and a rotatable lever 8 to admit coins to a storage box within the meter and start the timer. The interior of the meter also includes a locking mechanism, which may be comprised of an electromechanical latch mounted at any suitable location, for example near the top of the cover, having an arm and pawl normally extended to engage a corresponding flange on the front cover in order to lock the same in a closed position. When a coil associated with the latch is energized by a suitable voltage the arm and pawl are Withdrawn from the extended position to unlock the cover. The cover may then be pivoted about a bottom hinge to permit access to the interior of the meter in order to service the timing mechanism or empty the coin storage box.

A portable encoder device is shown including a flexible cable 17 which may be plugged into a receptacle 16 in the meter head in order to complete an electrical circuit between the encoder and a decoder circuit contained within the meter head. The encoder includes means for generating a predetermined code signal to which the decoder circuit is responsive, as well as a source of power, for example, a battery, to operate the meter locking mechanism.

In order to operate the meter lock, an operator would adjust the encoder to generate the predetermined code signal for the particular meter, connect the encoder with the meter head and switch on the encoder. The decoder circuit within the meter would detect the correct code signal and emit a command signal in response thereto. The command signal would be fed back to the encoder via a circuit within cable 17 and act to trigger the supply circuit of the encoder. When triggered, the encoder power source supplies sufiicient power to the latch coil be used to unlock a plurality of locks each having a different combination.

FIG. 2 shows a block diagram of a system according to the present invention including an encoder 20 and a decoder 21. The encoder shown includes three sine wave oscillators 22, 23, 24, each designed to oscillate at a different frequency. The outputs of all the oscillators are fed to a mixer 25. The mixer includes a battery or some other suitable D.C. power source, as well as switching means for providing either a low level D.C. output or a high level D.C. output. In the mixer the three wave inputs are superimposed on hte low level D.C. signal to form a code signal which is supplied to the decoder input. The D.C. component of the signal passes through a filter network comprised of resistor 27 and capacitor 28. However, the low level of D.C. voltage is insufficient to break down Zener diode 30 and, therefore, no D.C. signal is presented to the upper inputs of NAND gates 35 and 36.

The AC. components of the code signal pass through an isolation amplifier 3'8 and then to three parallel detector circuits 40, 41, 42. Each detector circuit includes an amplifier having a tuned circuit in its output stage. Each of the three tuned circuits is highly selective and is tuned to pass a different one of the three frequencies which comprise the correct coded signal. The outputs of the detectors are fed to a NAND gate 31. NAND gate 31 is designed to produce a 1 output when positive or 1 signals are present on its three upper inputs and a O is present on its fourth or bottom input. A 1 output from NAND gate 31 indicates the presence of a correct code signal input to the decoder and triggers one shot multivibrator 32. The output pulse from the multivibrator appears at a 1 at the lower input of NAND gate 35 and inhibits its operation. At the same time the multivibrator output pulse is fed back to the encoder as a command pulse and acts to trigger the mixer switch means whereby the high level D.C. output appears at the decoder input.

Presence of the high level D.C. signal breaks down the resistance of the Zener diode 30 and a 1 input is presented to the upper input of each of NAND gates 35 and 36. Since a gate 35 is inhibited and cannot produce an output, the lower input of gate 36 has a 0 input and that gate produces an output to amplifier 44. The amplifier output is fed directly to the actuator 45, which in the preferred embodiment is a coil associated with the electromechanical latch. Alternatively the electro-responsive element of the actuator may comprise any suitable solenoid, magnetic latch, solid state switch or signal light adapted to indicate the presence of a correct code signal.

\In the event the higher level D.C. signal is supplied prior to the coded signal, the Zener diode 30 will break down and NAND gate 35 will have a 1 signal on the upper input and a 0 signal on its lower input. This will cause that gate to produce a 1 output which will appear on the lower inputs of each of gates 31 and 36, thereby inhibiting both from operation and preventing the actuator from being energized. Likewise, if all frequencies of the code signal are not present or if the D.C. level should not be changed at the right time, then the actuator will remain quiescent.

FIG. 3 shows a schematic diagram of a sine wave oscillator circuit of the type used in the preferred embodiment of the encoder. The circuit includes oscillator transistor Q A circuit may be traced from terminal 50, connected to a suitable source of D.C. power, not shown, through resistor 51, terminal 52, inductor L the collector-to-emitter path of Q and through resistor 69 to ground. Capacitor C is connected from terminal 52 to ground and resistor 53 defines a current path between terminal 52 and the base of Q Resistor 54 connects the base of Q to ground and capacitor C connects the collector of Q to ground. Amplifier transistor Q has its collector-to-emitter path connected from terminal 50 through resistor 55 to ground. The base of Q receives the output of Q through resistor 56.

A circuit of amplifier transistor Q, is likewise traceable from terminal 50 through resistor 57, the collectorto-emitter path of Q through resistor 58 to ground. The base of Q receives the output of Q through resistor 59 while resistor 60 connects the base of Q to ground. A feedback path for the oscillator may be traced from the collector of Q along line 61 through capacitor C resistor 62, terminal 63, resistor 64, capacitor C to the base of Q. A pair of oppositely poled diodes 65, 66 are connected in parallel between terminal 63 and ground. The output of the circuit is taken from the emitter of Q along line 67 to terminal 68.

An unconventional feature of the oscillator is the addition of amplifier stage Q which serves to introduce a phase shift of 180 in the signal in the feedback path of the oscillator. This phase shift of the signal permits the system to oscillate without introducing a tap in either the inductor L or the capacitor C of the tank circuit, as would be necessary in the use of conventional Hartley or Colpitts oscillator circuits. The use of Q as an extra stage of amplification provides a very pure sine wave output at terminal 68. Resistor 62, and diodes 65, 66 comprise a limiter stage in the feedback loop. In order to compensate for the characteristics of the transistors used in the decoder it is desirable to have the oscillator output increase with a decrease in temperature. This is accomplished by selecting diodes of suitable temperature coefiicient for 65 and 66. However, other means of compensation could be used, for example, resistors 53 and 54 could be replaced by thermistors of proper values.

FIG. 4 shows a mixer and switching circuit of suitable design for use in the preferred embodiment of the invention. Terminals 100, 101, 102, receive the respective outputs of the three sine wave oscillators and serve as the inputs to the mixer circuit. A path may be traced from source terminal 110 through resistor 111, diode 112, terminal 113, diode 114, resistor 115 to ground. A parallel circuit path is available from source terminal 110 through the collector-to-emitter path of Q resistor 116, terminal 117, resistor 118, emitter-collector path of Q to ground. The base of Q is directly connected to the junction of resistor 111 and diode 112; while the base of Q is directly connected to the junction of resistor 115 and diode 114. An input circuit is available from terminal 100 through capacitor C and resistor 119 to terminal 113 and corresponding circuits are available from terminal 101 through capacitor C and resistor 120, and from terminal 102 through capacitor C and resistor 121, to the same terminal. A voltage supply circuit is defined from terminal 110 through resistor 122, terminal 123, Zener diode 124 to ground; terminal 123 thus becoming a constant source of DC. voltage for the oscillator supply terminal 50 in FIG. 3. The A.C. output of the mixer circuit is taken from terminal 117 through capacitor C to terminal 126.

The D.C. component of the encoder output is provided from a circut which includes another emitter-follower pair of transistors Q Q Thus, a circuit path may be traced from terminal 110 through the collector-to-emitter path of Q resistor 127, terminal 128, resistor 129, and through the collector-to-emitter path of Q to ground. A parallel circuit is defined from the collector of Q through resistor 130,, terminal 131, diodes 132 and 133, terminal 134 and resistor 135 to ground. The base of Q is directly connected to terminal 131 and the base of Q directly connected to terminal 134.

Transistors Q and Q form a complementary flipflop; the collector of Q being connected to the emitter of Q on through resistor to the emitter of Q and then through resistor 136 to ground. The collector of Q is connected through resistor 137 to the base of Q and the collector of Q is connected directly to terminal 131. A feedback circuit is available from terminal 128 through resistor 138, terminal 139, resistor 140, terminal 141, and resistor 142 to ground. The base of Q is connected directly to terminal 139 and terminal 141 serves as an input for a command signal from the decoder in a manner to be explained hereinafter.

FIG. 5 shows a schematic diagram of a decoder circuit used in the preferred embodiment of the invention. A positive line 200 and a grounded negative line 201 serve as inputs to the decoder. Three detector amplifier transistors Q Q Q are connected in parallel across lines 200, 201. The first stage includes a stabilizing resistor 203 connected between line 200 and the emitter of Q and a highly selective tuned circuit comprised of L C connected in parallel between the collector of Q and line 201. The second and third stages include, respectively, corresponding elements including resistor 204 and tuned circuits L C as well as resistor 205 and tuned circuits L22, C connected in a similar manner. A biasing network for the amplifier transistors includes diode 208, resistor 209, and resistor 210 connected in series between terminals 200, 201. A circuit may also be traced from the junction of resistors 209, 210 through resistor 211 to terminal 212 and through capacitor C to line 201. Terminal 212 is connected directly to each of the bases of Q Q21 and Q22- The output of decoder amplifier Q is taken from the collector of Q through resistor 215 and diode 216 to the base of Q In similar manner the output of Q is taken through resistor 217 and diode 218 to the base of Q while the output of Q passes through resistor 219 and diode 220 to the base of Q Resistor 222 isolates the decoder amplifier stages from the power circuits of Q O Q which comprise NAND gate inputs. A capacitor C is connected from line 200 to the common junction line 224 of the emitters of Q Q and Q which are grounded through line 201. A resistor 223 connects line 200 with the common junction line 225 of the collectors of Q Q Q Zener diode 227 connects junction line 225 to line 201.

The base of Q is connected to line 200 through resistor 228 and line 201 through capacitor C Resistors 229, 230 and capacitors C C are connected in similar manner with the bases of Q Q respectively. The common output of Q Q and Q is connected through resistor 232 to the base of switching transistor Q The emitter of Q is connected to line 200 while the collector is connected through resistor 233 to line 201. The output from Q is connected directly from the collector of Q to the base of switching transistor Q A power circuit may be traced from line 200 through the emitter-to-collector path of Q on through resistor 234 to negative line 201.

The output of Q is taken through diode 235 to terminal 236 which is returned to line 201 through capacitor C A feedback circuit may be traced from terminal 236 through diode 237 along line 238 to DET terminal 240. Another circuit is available from terminal 236 through resistor 241 to the base of switching transistor Q which is connected to line 201 through resistor 242 and diode 243. The emitter of Q is connected directly to negative line 201 and the collector of Q is connected through resistor 245 to the base of Q The emitter of Q is connected to line 200 and the collector is conected through the driving element of the actuator, for example, a coil, to negative line 201. The collector of Q is also connected directly to the junction of resistor 242 and diode 243.

The circuits as disclosed in FIGS. 3-5 operate in the following manner. The tank circuit elements and other components of each of the three sine wave oscillator circuits are selected so that the oscillators produce thre alternating curent signals of dilferent frequency which are fed to the mixer. The components of the tank circuits may be variable so that each oscillator may be adjusted to produce different frequencies in order to change the wave content of the code signal. The mixer includes the circuit branch including diode 112, 114 as well as the complementary emitter follower stage comprised of transistors Q and Q The output of the emitter follower stage is taken from terminal 117 and is comprised of a mixture of thre three A.C. input wave forms. The output signal from the encoder, consisting of a mixture of the three sine waves and the low D.C. level taken from terminal 126, is applied to positive line 200. From line 200 the code signal is available to each of the detector stages comprised of transistors Q Q and Q Each of the detector amplifier stages is designed to detect a different one of the three sine wave frequencies. Bias current is supplied to the bases of Q Q Q through a network consisting of diode 208, resistor 209, resistor 210, and filter capacitor C while resistors 203, 204 and 205 serve to stabilize the current drawn by each of the amplifier transistors and to control the input to each detector stage.

The presence of an alternating current signal at the outputs of the detector stages will be detected by diodes 216, 218 and 220 and applied to the bases of Q Q and Q The values of resistors 215, 217 and 219 are made sufiiciently high to cause each tuned output circuit to be highly selective. However, the presence of a signal of suflicient amplitude at the output of each of the decoder stages will cause normally conducting transistors Q Q and Q to be cut off. The cut 01f of all three of the switching transistors and the presence of only the low level D.C. supply at Zener diode 227 will remove the bias current at the base of Q This condition will permit normally conducting Q to cut off. It should be noted that presence of the high D.C. level at the input prior to or along with the coded signals will cause the breakdown of Zener diode 227 and prevent Q from cutting off, thereby prohibiting the remainder of the circuit from being actuated.

When Q is cut olf Q will begin to conduct and capacitor C will begin to charge through diode 235- When the voltage on C has risen by a sufiicient amount, Q will begin to conduct, the complementary flip-flop circuit comprised of Q Q will be triggered and the actuator driving element circuit will be opened. At the same time the flip-flop is triggered, a command signal will be sent back through diode 237 along feedback line 238 to DET terminal 240.

The high D.C. component of the encoder output signal which serves as an operating voltage for the actuator is supplied from a complementary emitter-follower pair of transistors Q Q Transistors Q and Q form a complementary set-reset flip-flop circuit. In the absence of a positive going signal at the detector DET terminal and when the power is applied to the flip-flop, transistors Q and Q are both non-conducting. During this state, the low D.C. output signal is supplied at terminal 128, determined by the voltage divider formed by resistors 130 and 135 shown here as being equal in magnitude and therefore dividing the supply voltage by two.

When a positive pulse of suflicient amplitude appears at the DET terminal 240 and is applied to the base of Q that device will conduct and thereby drive Q into conduction. As Q conducts the D.C. output level at terminal 128 will rise to nearly the full positive voltage. At the same time, this high D.C. output level is fed back to the base of Q through resistor 138 and will maintain Q in conduction even though the input voltage at the DET terminal drops to zero. The high D.C. output level is also passed through terminal 126 and along line 200 through the open emitter-to-collector path of Q to operate the actuator.

Although the embodiment of the present invention described herein includes three sine wave oscillators, it should be apparent that the code signal could, as well, be comprised of any other suitable number or combination of sine Wave and/ or pulse signals. For example, the code signal could be comprised of several Waves of the same frequency but staggered phase. Alternatively, a train of spaced digital pulses could be used as the coded signal. In any such alternative embodiment the decoder circuit would, in turn, be adapted to include the necessary circuit to detect the presence of a correct combination of the selected code.

The described embodiment also contemplates that an initially supplied low D.C. signal be switched to a high D.C. operating signal if desired, proper circuitry could be utilized to reverse this sequence so that the high D.C. level is used as a component of the preliminary signal and a low D.C. level as an operating voltage for the actuator.

I claim:

1. A code responsive apparatus comprising:

a first portable device comprising a source of electric power and a coded signal generator;

a second device, and separable circuit means for selectively connecting said portable device to said second device;

said second device having a decoder means, a command signal generator and an electrically operable actuator;

said circuit means serving to transmit a coded signal from said coded signal generator to said decoder means; said command signal generator being responsive to receipt of a properly coded signal by said decoder means to generate a command signal and transmit the same over said circuit means to said portable device; and

responsive means in said portable device, responsive to said command signal for connecting said source of electric power, through said circuit means, to said actuator to energize the same.

2. A code responsive system as described in claim 1 wherein said encoder means includes a plurality of generators each adapted to produce an electrical sine wave signal of different frequency and mixer means for combining the plurality of sine wave signals with a low level D.C. output from said source to constitute said code signal.

3. A code responsive system as described in claim 1 wherein said encoder means includes a plurality of generators each adapted to produce an electrical sine wave signal of different frequency and mixer means for combining the plurality of sine wave signals with a high level D.C. output from said source to constitute said code signal.

4. A code responsive system as described in claim 2 wherein said decoder means includes a plurality of amplifiers respectively tuned to detect said sine wave signals and logic circuit means receiving outputs from said amplifiers for producing an output signal when all of said plurality of sine wave signals are detected.

5. Apparatus as defined in claim 1 wherein said second device comprises a housing having a movable closure, a latch Within said housing normally holding said closure in closed position, said actuator being drivingly connected to said latch to release the same when said actuator is energized.

6. Apparatus as defined in claim 5 wherein said housing comprises a coin receiving means on a parking meter.

7. Apparatus as defined in claim 1 wherein said circuit means comprises a plurality of conductors extending from said portable device and defining a cable, a first connector portion on the end of said cable, and a mating connector portion on said second device.

8. Apparatus as defined in claim 1 wherein said portable device comprises a housing adapted to be manually transported, said source of electric power comprising 2,658,942 11/1953 Durkee.

a battery in said housing. 3,119,096 1/1964 Sparrow et a1.

References Cited HAROLD PITTS, Primary Examiner UNITED STATES PATENTS 5 US. Cl. XIR- 1,829,836 11/1931 Newby. 34 147 1 7 3 0 2,541,461 2/1951 Churchill. 

